How to get the latest and oldest record in mongoose.js (or just the timespan between them)

Question

Basic problem

I have a bunch of records and I need to get latest (most recent) and the oldest (least recent).

When googling I found this topic where I saw a couple of queries:

// option 1 Tweet.findOne({}, [], { $orderby : { 'created_at' : -1 } }, function(err, post) {   console.log( post ); }); // option 2 Tweet.find({}, [], {sort:[['arrival',-1]]}, function(err, post) {   console.log( post ); }); 

Unfortunatly they both error:

TypeError: Invalid select() argument. Must be a string or object. 

The link also has this one:

Tweet.find().sort('_id','descending').limit(15).find(function(err, post) {   console.log( post ); }); 

and that one errors:

TypeError: Invalid sort() argument. Must be a string or object. 

So how can I get those records?

Timespan

Even more ideally I just want the difference in time (seconds?) between the oldest and the newest record, but I have no clue on how to start making a query like that.

This is the schema:

var Tweet = new Schema({     body: String   , fid: { type: String, index: { unique: true } }   , username: { type: String, index: true }   , userid: Number   , created_at: Date   , source: String }); 

I'm pretty sure I have the most recent version of mongoDB and mongoose.

EDIT

This is how I calc the timespan based on the answer provided by JohnnyHK:

var calcDays = function( cb ) {   var getOldest = function( cb ) {     Tweet.findOne({}, {}, { sort: { 'created_at' : 1 } }, function(err, post) {       cb( null, post.created_at.getTime() );     });   }     , getNewest = function( cb ) {     Tweet.findOne({}, {}, { sort: { 'created_at' : -1 } }, function(err, post) {       cb( null, post.created_at.getTime() );     });   }    async.parallel({      oldest: getOldest   , newest: getNewest   }     , function( err, results ) {       var days = ( results.newest - results.oldest ) / 1000 / 60 / 60 / 24;       // days = Math.round( days );       cb( null, days );     }   ); } 

Answer 1

Mongoose 3.x is complaining about the [] parameter in your findOne calls as the array format is no longer supported for the parameter that selects the fields to include.

Try this instead to find the newest:

Tweet.findOne({}, {}, { sort: { 'created_at' : -1 } }, function(err, post) {   console.log( post ); }); 

Change the -1 to a 1 to find the oldest.

But because you're not using any field selection, it's somewhat cleaner to chain a couple calls together:

Tweet.findOne().sort({created_at: -1}).exec(function(err, post) { ... }); 

Or even pass a string to sort:

Tweet.findOne().sort('-created_at').exec(function(err, post) { ... }); 

Answer 2

Fast and Simple - One Line Solution

Get 10 latest documents

MySchema.find().sort({ _id: -1 }).limit(10) 

Get 10 oldest documents

MySchema.find().sort({ _id: 1 }).limit(10) 

In case you want sorting based on some other property i.e. createdAt and get the oldest or latest. It is similar to the above query.

MySchema.find().sort({ createdAt: -1 }).limit(10)  // 10 latest docs MySchema.find().sort({ createdAt: 1 }).limit(10) // 10 oldest docs